The main process flow of paper manufacturing comprises paper forming, pressing (including wiping, vacuum and dehydration) and drying. In the drying process, wet paper sheet is sandwiched between the dryer web and the drying cylinder, the wet paper on the surface of the drying cylinder is exerted a certain amount of pressure by the dryer web, the fibers in the wet paper layer form a larger contact area with the surface of the drying cylinder under the pressure of the dryer web, and under the action of the high temperature and pressure of the surface of drying cylinder, the moisture in wet paper sheet is rapidly evaporated to reach the purpose of page drying. With the development of papermaking technology, paper machine manufacturers have successfully invented the shoe-type press technology. This technology can successfully expand the press area of paper machine to 20 times the original, the pressure area can reach more than 100 mm, the paper machine speed can reach 3,000 m/min, while the speed of the paper machine is improved, the requirement of the manufacturing technology of the dryer web is also improved correspondingly.
When the paper machine runs at a high speed, that is, when the machine runs at a speed over 800/minute, any defect on the surface of the dryer web will have an impact on the paper sheet, resulting even rupture of the paper sheet and stopping the machine. Especially in single-hung or single-row dryer parts of the first group and the second group in the paper machine, where the moisture of the wet paper layer is larger and the paper sheet is extremely easy to break. The existing dryer webs are single-layer fabrics that often run off an upper surface due to a yarn ends, resulting in the waste of tons of paper and significant waste.
In addition, because of the unreasonable structure, sometimes the tension of the web edge and the tension of the web body are often inconsistent. When the tension is too loose or too tight, the normal operation of the paper machine and the drying effect of the paper sheet will be affected, and even the edge of the paper will be damaged or broken, leading to premature disembarkation of the dryer web, seriously affecting the production and resulting in economic losses. The existing structure of dryer webs for paper manufacturing, some have only one layer, some have two layers, but since the upper and lower layer of the structure are different and have no complementarity, the overall structure is of poor consistency, the structural stability is poor, at the same time, it is very easy to produce stress concentration, so as to break or destroy the surface quality of paper.
Moreover, in the process of paper drying, the paper must be kept flat, but the dryer section of the paper machine requires that dry web must have terminal seams, some of the seams are not smooth, resulting in seam traces, as well as a “seersucker” and other convex and uneven paper disease. In the installation process, if the tension consistency of the seam loops is poor, which can also cause the crease of the dry web and affect the quality of papermaking. The air permeability of the dry web seam is too large or too small, which will also lead to paper breakage in high speed operation and affect papermaking efficiency of the paper machine.
At present, the common designs of the dry webs in the market are divided into two categories. The first category is that the warp yarn system is in an upper and lower penetrating direction and interlace with the weft yarn system to form a woven texture; the second category is that the warp yarn system is an upper and lower of the tape yarn design, warp yarn system of the upper flat yarns interlace with the weft yarn system on the upper layer; warp yarn system of the lower flat yarns interlace with the weft yarn system on the lower layer.
In the dryer web seam, whether it is the pin loop seam or the spiral loop seam, all the warp yarns after being return-plugged form a 4-row butted breakpoints in the cross direction (CD) on the back of the dryer web. The yarn ends of these butted breakpoints, as the damaged paper sheet will be wrapped around the drying cylinder or guide roller in the operational process of dryer web, resulting in an excessive local stress and that dryer web will be over-stretched. The butted breakpoints on the back of the part of the over-stretched dryer web will return to the front of the dryer web, resulting the paper sheets to be scratched and forming holes in the surface of the paper sheets. In the paper-making market in Korea, some papermakers once returned the purchased dryer webs due to such defects on paper sheets, which causes huge losses to paper providers and dryer web providers.
All these kinds of things happen frequently in the existing technology, people are trying to find solutions, but they have never been completely solved, which has seriously affected the quality of paper making and the improvement of efficiency. As the rejection rate is high, the production cost is greatly increased.